Reflections on the Origin of the EMC Effect

TL;DR

This paper reviews two main theories explaining the EMC effect, emphasizing the potential of spin-dependent measurements at Jefferson Lab to distinguish between them and deepen understanding of nuclear structure.

Contribution

It compares mean-field and short-range correlation models for the EMC effect and highlights the importance of spin-dependent measurements to differentiate these theories.

Findings

Predictions for the spin-dependent EMC effect vary significantly between models.

Measuring the spin-dependent EMC effect can clarify the role of short-range correlations.

The study underscores the potential of Jefferson Lab experiments to resolve the EMC effect puzzle.

Abstract

In the 35 years since the European Muon Collaboration announced the astonishing result that the valence structure of a nucleus was very different from that of a free nucleon, many explanations have been suggested. The first of the two most promising explanations is based upon the different effects of the strong Lorentz scalar and vector mean fields known to exist in a nucleus on the internal structure of the nucleon-like clusters which occupy shell model states. The second links the effect to the modification of the structure of nucleons involved in short-range correlations, which are far off their mass shell. We explore some of the methods which have been proposed to give complementary information on this puzzle, especially the spin-dependent EMC effect and the isovector EMC effect, both proposed by Cloet, Bentz and Thomas. It is shown that the predictions for the spin dependent EMC effect, in particular, differ substantially within the mean-field and short-range correlation approaches. Hence the measurement of the spin dependent EMC effect at Jefferson Lab should give us a deeper understanding of the origin of the EMC effect and, indeed, of the structure of atomic nuclei.